Micro of Staph - Cross

Question 1

What do all Staph have that helps you identify them vs. strep?

Answer 1

Catalase (can degrade H2O2)

Question 2

What type of infection(s) does Staph epidermidis normally cause?

Answer 2

Prosthetic hardware/IV catheter infections, endocarditis

Question 3

What type of infection(s) does Staph saprophyticus cause?

Answer 3

UTI; 2nd most common cause

Question 4

People with arthritis or other joint damaging diseases are at increased risk for osteomyelitis. Why?

Answer 4

Joint damage exposes underlying fibronectin/laminin, Staph aureus can easily adhere to the glycoproteins

Question 5

What area of the skeleton is especially vulnerable for osteomyelitis due to arthritis?

Answer 5

The vertebral column (lumbar especially)

Question 6

What is the carrier state?

Answer 6

Individual harbors a potential pathogen and can be a source of infection for others

Question 7

What is colonization?

Answer 7

Acquisition of a new organism and it may cause infection

Question 8

What is colonization resistance?

Answer 8

Nonpathogenic resistant bacteria occupy attachment sites interfering with pathogenic bacterial colonization

Question 9

Gram stain of S. aureus?

Answer 9

Gram positive cocci in clusters (grapelike)

Question 10

Morphology of S. aureus?

Answer 10

Beta hemolytic; catalase(+), coagulase(+), ferments mannitol

Question 11

What gene contains the sequence for the altered PBPs that confers methicillin resistance?

Answer 11

MecA

Question 12

What serum do they use in the lab for the coagulase test?

Answer 12

Rabbit serum (she said to know this)

Question 13

Where is the main site of colonization (on the body) for S. aureus?

Answer 13

The nose

Question 14

Name all the S. aureus virulence factors (there are 10)

Answer 14

1) Staphyloxanthin
2) Coagulase
3) Hemolysins
4) Portein A
5) Teichoic Acid
6) Polysaccharide capsule
7) Peptidoglycan
8) Alpha toxin/Hemolysin
9) Panton Valentine (P-V) leukocidin
10) Gamma toxin/leukotoxin

Question 15

What does staphyloxanthin do? What does it specifically do to the bacteria when on agar?

Answer 15

It inactivates superoxides produced by WBCs; it confers the gold color unique to S. aureus

Question 16

What does coagulase do?

Answer 16

converts prothrombin–>thrombin; this delays neutrophil migration

Question 17

What do hemolysins do?

Answer 17

Hemolyse RBCs and use their Fe2+ to grow

Question 18

What does Protein A do?

Answer 18

Binds to the Fc portion of IgG to prevent complement activation; no C3b is produced so phagocytosis is greatly impaired

Question 19

What do teichoic acids do?

Answer 19

Mediate the adherence of staph to mucosal cells

Question 20

What does peptidoglycan do?

Answer 20

Stimulates macrophages to produce cytokine storm/activate complement; causes the “septic shock” picture seen in S. aureus bacteremia

Question 21

What does P-V leukocidin do?

Answer 21

Pore forming cytotoxin that kills leukocyte by cell membrane disruption and causes tissue necrosis

Question 22

What diseases specifically does P-V leukocidin allow S. aureus to cause?

Answer 22

Necrotizing PNA and severe soft tissue/skin infection

Question 23

What does gamma-toxin/leukotoxin do?

Answer 23

Lyses phagocytes/RBCs

Question 24

What bacteria almost always causes an abscess?

Answer 24

S. aureus

Question 25

What virulence factors cause scalded skin syndrome?

Answer 25

Exfoliative toxins A and B

Question 26

What age group is scalded skin syndrome commonly seen in?

Answer 26

Newborns, 3-7 days of age

Question 27

What do exfoliative toxins A and B do to the body?

Answer 27

Protease that cleaves desmoglein; separates the epidermis at the granular layer

Question 28

What toxin causes S. aureus induced food poisoning? Describe the illness

Answer 28

Enterotoxin A; vomiting and watery, NON-BLOODY diarrhea

Question 29

Why is enterotoxin A so virulent?

Answer 29

It is heat resistant (brief cooking won't destory it) and it is resistant to stomach acids

Question 30

Describe bullous impetigo

Answer 30

Seen in young children; flaccid bullae with clear yellow fluid that later becomes more turbid; rupture will leave behind a thin brown crust, commonly on the TRUNK

Question 31

What is the pathogenesis of Staph toxic shock syndrome?

Answer 31

Toxin mediated/superantigen, elicits large amount of IL-1, IL-2, and TNF-a release

Question 32

Common scenarios causing staph toxic shock syndrome?

Answer 32

Tampon use, nasal packing to stop epistaxis, post-op infection

Question 33

Blood cultures in Staph aureus toxic shock syndrome?

Answer 33

NEGATIVE 95% of the time

Question 34

Lethal complication of toxic shock syndrome, commonly seen in bacteremia (I know this question sucks)?

Answer 34

DIC

Question 35

Resistance seen in MRSA (mechanism of resistance)?

Answer 35

Change in PBPs in the cell membrane

Question 36

Resistance seen in VRSA (mechanism of resistance)?

Answer 36

D-ala replaced with D-lactate; vancomycin can no longer affect it

Question 37

Resistance seen in VISA (mechanism of resistance)?

Answer 37

Synthesis of unusually thickened cell well

Question 38

What is the D-test?

Answer 38

Culture bacteria on a plate with a disk of clindamycin and one of erythromycin. If area around the clinda is "D-shaped" the test is +, indicates inducible resistance (DON'T USE CLINDA)

Question 39

Generalized tx guidelines for Toxic shock syndrome?

Answer 39

Aggressive fluid replacement therapy, vasopressors (can cause distal necrosis). Abx and surgical debridement, if necessary

Question 40

Why do you use clindamycin in the treatment of TSS? What other abx shares the same function?

Answer 40

It suppresses toxin synthesis; can also use Linezolid

Question 41

Morphology of Staph epidermidis?

Answer 41

Catalase(+), Coagulase(-), non-hemolytic, urease(+), does NOT ferment mannitol, Novobiocin sensitive

Question 42

What is the main pathogenic mechanism of staph epidermidis?

Answer 42

It has adhesins for interaction with surface proteins; once it attaches to a catheter or prosthetic device it secretes a polysaccharide biofilm (insulates it from phagocytosis/abx)

Question 43

You get a blood culture positive for Staph epidermidis. The patient is afebrile and in no distress. What do you think?

Answer 43

Contamination; Staph epi is all over the skin and commonly contaminates blood cultures

Question 44

Staph saprophyticus morphology?

Answer 44

Catalase(+), Coagulase(-), non-hemolytic, urease(+), does NOT ferment mannitol, Novobiocin resistant

Question 45

Novobiocin test. Distinguishing between which bacteria?

Answer 45

Staph epidermidis (SENSITIVE) vs. Staph saprophyticus (RESISTANT)

Question 46

What 2 morphologic characteristics distinguish S. aureus form all other staphylococci?

Answer 46

Coagulase (+) and B-hemolysis

Question 47

Pathogenesis of enterotoxin-A mediated food poisoning

Answer 47

Superantigen in the GI tract, causes massive IL-1 and IL-2 release from macrophages/helper T cells